Executes the systematic ACP -> A2A module rename per ADR-047.
- Renamed all legacy ACP references to A2A throughout cleveragents.a2a module
- Standardized all 22 exported symbols to A2A naming conventions
- Added BDD test suite validating export completeness, zero ACP remnants, and documentation accuracy
Closes#10583
Parent Epic: #8569 (A2A Standard Adoption)